Modern mobile telephones provide a rich set of features including video conferencing wherein a Circuit Switched Data (CSD) call is established between two subscribers. During the data call, video coded data is transferred over a CSD connection and decoded at the recipient terminal. A pair of CSD channels is established on the call setup to accommodate video data terminating to each of the two subscribers.
The establishing of the CSD call is time consuming in the present mobile communications systems which comply with 3GPP standards. While the data call is being built, there is no audio channel to use for relaying the normal ring back tone to calling subscriber as indication of the ringing at call recipient. Hence, the originating subscriber (A-subscriber) may be provided with a locally produced ring back tone by terminal.
In normal mobile phone speech calls, it is possible to relay a selective ring-back tone to the caller whilst the phone call is being established (while waiting for the B-subscriber to answer her phone). The selective ring back tone is a service that is typically offered as called subscriber side service in present 2G and 3G mobile communication networks for voice calls. A traditional ring back tone (“beep beep . . . ”) is replaced by more attractive and personalized music tone, which can be played while the called party's terminal is being alerted. When the called subscriber answers to incoming call, the music tone is stopped and through-connection between caller and called subscriber is established by the telecommunications network.
The mechanism typically used to provide selective ring back tone service for voice calls is not, however, suitable as such to the afore described video calls due to the lack of suitable audio channel while the CSD channels are being established for a video call.
Moreover, typically Circuit Switched (CS) core network has no mechanism to terminate user plane related protocols and participate on video call specific negotiations on items such as codecs, master-slave, logical channels. Therefore, video calls are not terminated within CS core network, e.g. to Mobile Switch Centre (MSC) or Media Gateway (MGW), to be subsequently continued towards intended recipient.
Current and likely also forthcoming 3G-H324M compliant video enabled terminals do not support protocol re-negotiation at user plane level. This means in practise that if a video call were first answered by the CS core network, for instance, and ITU-H.223 and ITU-H.245 level protocol negotiations were thus successfully completed, it would be no longer possible for the video call recipient's user equipment to re-negotiate the video call specific items. The calling subscriber's terminal assumes that properties once negotiated between the calling subscriber's terminal and another peer ITU-H.223/ITU-H.245 entity remain unchanged throughout the video call.
Worse still, video call establishment includes both bearer set-up as well as user plane protocol establishment that is done after end-to-end connection through the Circuit Switched (CS) core network has been established. Hence, typically the establishment of a video call takes longer to complete than establishment of normal voice call.
CN1671160 discloses a method for realizing ring back tone and image thereof for picture phone service in mobile communication field, which contains a core network adopting calling subscriber supported phonetic and image decoding form which are resolved or preliminary arranged in calling subscriber start calling, playing ring back tone and image to calling subscriber through phonetic and image channel in Video Phone (VP) telephone series, said invention can uniformly customize ring back tone and provides its image to VP service in 3G system. This method is, however, only usable when the ring back tone and image can be transmitted over a video connection pre-established end-to-end to the called terminal.
U.S. Pat. No. 4,939,767 discloses that image data can be sent during a call establishment procedure. This publication discloses a particular arrangement in which two modems can start relaying image data faster than pre-existing fax devices. In that publication, the two modems first handshake through an open audio connection that serves as a bearer. Hence, the bearer connection is already established before the image data transfer can be started.
There millions of commercially available terminals capable of placing mobile video calls. Any changes to the existing terminals are time consuming and costly to implement.
Hence, there is a need to provide new approach to handle network configuration which would avoid and/or mitigate the problems associated with the present technology.